Optical identification element having non-waveguide photosensitive substrate with diffraction grating therein

ABSTRACT

An optical identification element (also known herein as a microbead) that is made from pieces of an optical fiber or substrate that includes an inner core or region being surrounded by an outer cladding region. The optical fiber or substrate has an identification code imparted therein containing coded information. The identification code may be in the form of a Bragg grating inscribed or written in either the inner core or outer cladding. The optical identification element may be microscopic in size having a length in a range of 1-1,000 microns or smaller; or for larger applications may have a length of 1.0-1,000 millimeters or more. The outer diameter may be as small as less than 1,000 microns, as well as in a range of 1.0 to 1,000 millimeters for larger applications.

CROSS REFERENCES TO RELATED APPLICATIONS

This application relates and claims benefit to the following U.S.provisional patent application Ser. No. 60/546,445 (CV-0035PR), entitled“Optical Identification Element Having Non-Waveguide PhotosensitiveSubstrate With Bragg Grating Therein”, filed Feb. 19, 2004, which ishereby incorporated by reference in its entirety.

This application also relates to U.S. provisional patent applicationSer. Nos. 60/546,435 (CV-0053PR), entitled “Multi-Well Plate WithAlignment Grooves for Encoded Microparticles”; and 60/547,013(CV-0065PR), entitled “Optical Identification Element Using Separate orPartially Overlapping Diffraction Gratings”, all filed Feb. 19, 2004 andhereby incorporated by reference in their entirety, as well as11/063,665(CV-0053US), entitled “Multi-Well Plate With Alignment Groovesfor Encoded Microparticles”, and 11/063,666, (CV-0065US), entitled“Optical Identification Element Using Separate or Partially OverlappingDiffraction Gratings”, and PCTUS/2005005745 “Optical IdentificationElement Using Separate of Partially Overlapping Diffraction Bratings”all filed Feb. 22, 2005 contemporaneously with the instant applicationand all also hereby incorporated by reference in their entirety.

The following cases contain subject matter related to that disclosedherein and are incorporated herein by reference in their entirety: U.S.Provisional Patent Application Ser. No. 60/441,678, filed Jan. 22, 2003,entitled “Hybrid Random Bead/Chip Microarray”, U.S. patent applicationSer. No. 10/645,689, filed Aug. 20, 2003, entitled “DiffractionGrating-Based Optical Identification Element”, U.S. patent applicationSer. No. 10/645,686 filed Aug. 20, 2003, entitled “End Illuminated BraggGrating based Optical Identification Element”, U.S. patent applicationSer. No. 10/661,234, filed Sep. 12, 2003, entitled “DiffractionGrating-Based Optical Identification Element”, U.S. patent applicationSer. No. 10/661,031, filed Sep. 12, 2003, entitled “End IlluminatedBragg Grating based Optical Identification Element”, U.S. patentapplication Ser. No. 10/661,082, filed Sep. 12, 2003, entitled “Methodand Apparatus for Labeling Using Diffraction Grating-based EncodedOptical Identification Elements”, U.S. patent application Ser. No.10/661,115, filed Sep. 12, 2003, entitled “Assay Stick”, U.S. patentapplication Ser. No. 10/661,836, filed Sep. 12, 2003, entitled “Methodand Apparatus for Aligning Microbeads in order to Interrogate the Same”,U.S. patent application Ser. No. 10/661,254 filed Sep. 12, 2003,entitled “Chemical Synthesis Using Diffraction Grating-based EncodedOptical Elements”, U.S. patent application Ser. No. 10/661,116 filedSep. 12, 2003, entitled “Method of Manufacturing of a Diffractiongrating-based identification Element”, U.S. Provisional patentapplication Ser. No. 60/519,932, filed Nov. 14, 2003, entitled,“Diffraction Grating-Based Encoded Microparticles for MultiplexedExperiments”, and U.S. patent application Ser. No. 10/763,995 filed Jan.22, 2004, entitled, “Hybrid Random bead/chip based microarray”.

BACKGROUND OF INVENTION

1. Technical Field

The present invention relates to an identification element, and moreparticularly to an optical identification element having a diffractiongrating written therein.

2. Description of Related Art

Many industries have a need for uniquely identifiable objects or for theability to uniquely identify objects, for sorting, tracking, and/oridentification/tagging. Existing technologies, such as bar codes,electronic microchips/transponders, radio-frequency identification(RFID), and fluorescence and other optical techniques, are ofteninadequate. For example, existing technologies may be too large forcertain applications, may not provide enough different codes, or cannotwithstand harsh temperature, chemical, nuclear and/or electromagneticenvironments. Therefore, it would be desirable to obtain a codingelement or platform that provides the capability of providing many codes(e.g., greater than 1 million codes), that can be made very small,and/or that can withstand harsh environments.

SUMMARY OF INVENTION

In its broadest sense, the present invention provides a new and uniqueoptical identification element (also known herein as a microbead) madefrom pieces of an optical fiber or substrate that includes an inner coreor region being surrounded by an outer cladding region, the opticalfiber or substrate having an identification code imparted thereincontaining coded information. The identification code may be in the formof a Bragg grating inscribed or written in either the inner core orouter cladding.

The optical identification element may be microscopic in size having alength in a range of 1-1,000 microns or smaller; or for largerapplications may have a length of 1.0-1,000 millimeters or more. Theouter diameter may be as small as less than 1,000 microns, as well as ina range of 1.0 to 1,000 millimeters for larger applications. Usingmanufacturing techniques developed in conjunction with the developmentof the present invention, one optical fiber or substrate can be drawnand processed to produce hundreds of thousands, as well as even amillion or more of such unique microbeads.

Microbead Using Conventional Waveguide Technology

In one embodiment, the optical identification element may bemanufactured from a conventional waveguide used in thetelecommunications industry in which the refractive index of the core ishigher than the cladding using, for example, the technique shown anddescribed in patent application Ser. No. 10/661,234 (CC/CV-0648A/0039A),which is hereby incorporated by reference, as well as other techniquesdescribed below. In this case, the Bragg grating is written in the coreof the conventional waveguide.

In this embodiment, conventional waveguides are used that are known inthe art and used in the telecommunications industry, which are made fromoptical fiber (e.g. 125 micron optical fiber). Conventional fiber Bragggratings are primarily formed in single mode fibers and are used forcoupling forward propagating modes into backward propagating modes. Thecoupled modes are confined to propagate in the core region of the fiberalong its axis; such a constraint defines a waveguide. If only one modeis allowed to propagate then the fiber is called a single modewaveguide, if two or more modes are permitted to propagate the fiber isreferred to as a multimode waveguide. The key to the function of guidingany number of modes in a fiber is the existence of both a core regionand a cladding region, where the refractive index of the core is higherthan the cladding. Conditions for single mode propagation are met whenthe V number of the fiber is less than 2.405, larger values will resultin more than one mode. The V number is related to the geometry andrefractive indices of the core and clad by the following relationship:

$\begin{matrix}{V:=\frac{2{\pi \cdot a \cdot {NA}}}{\lambda\; c}} & \; & \; & {{NA}:=\sqrt{{n1}^{2} - {n2}^{2}}}\end{matrix}$where n1 and n2 are the refractive indices of the core and cladrespectively. Practical single mode fibers are restricted to NA's in therange of 0.05 to 0.3. Fibers on the high end of the NA range haveextremely small core diameters, ranging from 1 to 3 microns, whilefibers on the low end of the range have larger cores, but theirsensitivity to bend loss increases substantially. As the NA approacheszero, the fiber behaves less and less like a waveguide, which isinconsistent with the stringent demands of the telecommunicationsindustry.

The broad list of devices and applications of fiber Bragg gratings hasthus far been restricted to operation in single or few moded fibers;these include band pass optical filters, strain sensors, dispersioncompensators, and gain flattening filters. In addition to the techniqueshown and described in patent application Ser. No. 10/661,234(CC/CV-0648A/0039A), the following list includes United States patentsdisclosing techniques for forming Bragg gratings in a conventionaltelecommunications waveguide:

1. U.S. Pat. No. 5,367,588—Method of fabricating Bragg gratings using asilica glass phase grating mask and mask used by same, by Ken Hill;

2. U.S. Pat. No. 5,327,515—Method for forming a Bragg grating in anoptical medium, by Dana Anderson; and

3. U.S. Pat. No. 5,351,321—Bragg grating made in optical waveguide, byElias Snitzer, which are all hereby incorporated by reference.

Microbead Using A New and Unique Optical Substrate

However, using such a conventional telecommunications waveguide to makesuch optical identification elements may be expensive to manufacturebecause the manufacturing techniques for making conventionaltelecommunications waveguides involve drawing optical fiber from apreform under strict predefined optical conditions so as to produceoptical fiber having strict predetermined optical characteristics.Moreover, using such a conventional telecommunications waveguide to makesuch optical identification elements may also be expensive tomanufacture because the manufacturing techniques for making suchconventional telecommunications waveguides involving writing stronggratings in the optical fiber with grating writing techniques requiringvery precise and expensive lasers in order to meet the demands of thetelecommunications industry. In view of this, the inventor has alsodeveloped an alternative optical identification element in which asubstrate is used such as an optical substrate having the refractiveindex of the core less than or equal to the cladding, that has importantadvantages in that it is less expensive to manufacture than when usingthe conventional waveguide technology otherwise used in thetelecommunications industry.

In this alternative embodiment, the optical identification element ismanufactured using, for example, the technique shown and described inU.S. patent application Ser. No. 10/661,234 (CC/CV-0648A/0039A), as wellas other techniques described herein.

Since in a typical usage, the optical identification element isinterrogated from the side in order to read the coded informationcontained in the Bragg grating, the Bragg grating may be written notonly in the core, but also in the cladding.

The microbeads in the alternative embodiment can be manufactured usingthe same process for inscribing Bragg gratings as those described insome of the above patents. Moreover, due to fact that the beads areinterrogated from the side, it is not necessary that the opticalsubstrate be manufactured to perform as a conventional waveguide. It isalso well known that the incorporation of Boron as a dopant enhances thephotosensitivity of the optical substrate to UV radiation. Boron is alsoknown as an index depressor when it is incorporated into silica glass.When designing a single mode waveguide the amount of Boron is usuallyvery carefully balanced with Germanium to provide the correct indexprofile in conjunction with enhanced photosensitivity. Again, becausethe requirement for waveguiding is removed for the microbeadapplications, excess amounts of Boron can be incorporated into the glassto increase its photosensitivity without regard to its optical guidingproperties. This has the benefit of reducing the cost of manufacturingthe optical substrate when compared to manufacturing the conventionalwaveguide, and increasing the photosensitivity without concern fortradeoffs involving other waveguiding issues.

When an optical substrate does not have to perform as a conventionalwaveguide, the core index of the optical substrate may be made lowerthan the cladding index. Under these conditions, the above equationdemonstrate that the NA is imaginary, and thus the optical substrate isnot considered a waveguide.

In the alternative embodiment, the optical identification element is anon-waveguide optical substrate having the Bragg grating inscribedtherein. The optical identification element structure consists of aphotosensitive region in the geometric center of the element surroundedby a non-photosensitive and non-absorbing region. The photosensitiveregion has an index of refraction less than or equal to the surroundingregion, thus preventing the element from supporting any modes. Thephotosensitive region is also designed to produce the appropriate Braggenvelope when interrogated from the side. Bragg envelopes in the rangeof 1 to 10 degrees are desirable for most microbead applications. Inorder to achieve such an envelope with visible light, the diameter ofthe photosensitive region must be no larger than 30 um, and for mostapplications the ideal size is approximately 12 um. Due to this smallsize and the practical issues that would arise from fabricating andhanding such a small optical identification element, it is convenient toinclude an outer region, which is neither photosensitive nor absorbing,which has an outer diameter between 50-130 um. The opticalidentification element had a core diameter of 24 um when the outerdiameter was 125 um, and a core diameter of 12 um when it was drawn to65 um in diameter. The index of the core region was −0.003, thusensuring the optical identification element would not guide a mode.

The New and Unique Optical Substrate Specification

The new and unique optical substrate may take the form of aphotosensitive non-waveguide optical fiber consisting of two sections,an outer section and at least one inner section. The outer section (orcladding) is made entirely of fused silica, without any dopants;however, trace amounts of impurities commonly found in fused silica ornatural fused quartz are acceptable. The inner section (or core) is madeof Germanium and Boron doped fused silica. The exact constituents ofBoron and Germanium are determined based on the desired refractive indexprofile (RIP). In one example, the photosensitive non-waveguide opticalfiber may have an outer diameter of 28 um±1 um, and the inner sectiondiameter of 8 um±0.5 um. The scope of the invention is intended toinclude using other dimensions as well.

The photosensitive non-waveguide optical fiber may be made by drawing aglass preform on a known fiber draw tower. Also, the photosensitivenon-waveguide optical fiber may be drawn with an outer coating or bufferlayer to protect the fiber during handling, e.g., a polymer basedcoating or other coating.

The RIP of the preform is used to calculate the following parameters ofthe photosensitive non-waveguide optical fiber as follows:Fiber Core Diameter=(Fiber Outer Diameter)/Ratio, where Ratio=(PreformOuter Diameter)/(Preform Core Diameter); the Ratio stays the same forthe Preform and the Fiber.Measurements are typically taken along the length of the preform inintervals of about 1 cm; however, other intervals may be used ifdesired. The Delta refractive index (or Delta Index) between the outercladding and the inner core is typically defined as the difference: Cladindex—Core index. In one example, the Delta Index may be greater than0.001 as measured from the preform RIP (and as will also exist in thefiber). Other values for the Delta Index may be used if desired.

The elemental (or dopant) constituents (Germanium and Boron dopants) inthe core may be about 20 mole % Germanium (Ge) and about 10 mole % Boron(B). Other percentages of the dopants may be used if desired. TheGermanium helps increase photosensitivity and the Boron reduces therefractive index to create the depressed core shape of the fiberrefractive index profile. Other values of Ge and B may be used providedthe inner core region has a refractive index that is less than the outercladding region (“depressed core”). Also, other dopant(s) now known orlater developed may be used to create the depressed core substrate.Also, instead of depressing the refractive index of the core, therefractive index of the cladding may be increased to create the desireddepressed core condition. In such a depressed core condition, light willnot be guided along the inner core region because it does not satisfythe well known waveguide condition; thus, the substrate does not act asa waveguide. Furthermore, the substrate will not propagate light alongthe core that could be reflected or diffracted by a diffraction gratinglocated in the substrate.

As discussed herein, the substrate may be photosensitive to impress thediffraction grating therein. In that case, the fiber inner region (orcore) has a photosensitivity that allows for a refractive indexmodulation of greater than about 5×10⁻⁴, using approximately 248nanometer (nm) light, and about 0.5 Joules/cm². Other levels ofphotosensitivity may be used, provided it is sufficient to give thedesired grating profile. The photosensitivity may be achieved by anytechnique now known or later developed that allows the region of thesubstrate where the diffraction grating is to be written to experience achange in the refractive index of the substrate material when exposed toincident radiation of a desired wavelength, e.g., Ultraviolet (UV)exposure or actinic radiation or other wavelength radiation. Forexample, the fiber may be loaded with Hydrogen (H₂) or Deuterium (D₂),or doped with lead, boron germanium, flame brushing, tin-germanium orother dopants, such as is described in U.S. Pat. No. 5,287,427 issued toAtkins on Feb. 25, 1994; or U.S. Pat. No. 5,325,659 issued to Atkins etal. on Aug. 10, 1993; or U.S. Pat. No. 5,157,747 issued to Atkins et al.on Oct. 20, 1992; or U.S. Pat. No. 6,221,566 issued to Kohnke et al. onApr. 24, 2001; or U.S. Pat. No. 6,327,406 issued to Cullen et al. onDec. 4, 2001; or U.S. Pat. No. 6,097,512 issued to Ainsle et al. on Aug.1, 2000; or U.S. Pat. No. 6,075,625 issued to Ainsle et al. on Jun. 13,2000; or U.S. Pat. No. 5,495,548 issued to Hill on Feb. 12,1996; or U.S.Pat. No. 6,436,857 issued to Brubeck et al. on Aug. 20, 2002; or asdescribed in articles by X-C Long et al., entitled “LargePhotosensitivity in Lead Silicate Glasses”, FE3-1/219 to FE3-3/221; orF. Ouellette et al, Applied Physics Letters, Vol. 58(17), p 1813; or G.Meltz et al, SPIE, Vol. 1516, “Int'l Workship on PhotoinducedSelf-Organization in Optical Fiber”, May 10-11, 1991, Quebec City,Canada, pp 1516-1518; or D. McStay, SPIE, Vol. 1314, “Fibre Optics '90”,pp.223-233; or as also discussed in the book by Kashyap, entitled “FiberBragg Gratings”, including Chapter 2, pp 13-54, Academic Press 1999; oras described in the references of one or more of the foregoing documentsreferred to therein, each of which is hereby incorporated herein byreference in its entirety; or some combination of the aforementioneddocuments.

While the substrate has been described as being used with a cylindricalfiber geometry, it should be understood and appreciated that othergeometries may be used, such as planar, D-shaped, or any other shape,such as is described for example in the aforementioned co-pendingco-owned patent applications. Also, when the material is referred to asa photosensitive material it is understood to mean any material whoseindex of refraction can be changed by exposing the material to light ofa predetermined intensity at a wavelength in a predetermined range.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of exemplary embodiments thereof, as illustrated in theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The drawing includes FIGS. 1-10, which are not drawn to scale, andinclude the following:

FIG. 1 is a side view of an optical identification element in accordancewith the present invention.

FIG. 2 is a top level optical schematic for reading a code in an opticalidentification element in accordance with the present invention.

FIG. 3 is a schematic of Bragg grating envelope measurement equipmentthat may be used to read an optical identification element according tothe present invention.

FIG. 4 includes FIG. 4( a) which shows a schematic of the fiber geometryof an optical fiber or substrate according to the present invention, andFIG. 4( b) which shows the refractive index profile in relation to theradius in microns of the fiber or substrate.

FIG. 5 shows a graph of a Bragg envelope measurement for depressed corefiber with 7 collocated gratings (65 μm, 13 μm core), having theintegrated peak power (arbitrary units) plotted in relation to the angle(degrees) of incidence.

FIG. 6 shows a refractive index profile for a substrate having an outerdiameter (OD) of 125 μm and a core diameter of 25 μm, having therefractive index difference plotted in relation to the X or Y position.

FIG. 7 shows a refractive index profile for a substrate having an outerdiameter (OD) of 65 μm and a core diameter of 14 μm, having therefractive index difference plotted in relation to the X or Y position.

FIG. 8 shows a refractive index profile for a preform having an outerdiameter of 13 mm and a core having a diameter of 3 mm.

FIG. 9 shows a refractive index profile for a preform having an outerdiameter of 12 mm and a core having a diameter of 2.4 mm.

FIG. 10 shows a refractive index profile for a preform, showing thedelta index in relation to the preform core diameter and the preformouter diameter.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1: The Basic Invention

Referring to FIG. 1, a diffraction grating-based optical identificationelement 8 (or encoded element or coded element) comprises a knownoptical substrate 10, having an optical diffraction grating 12 disposed(or written, impressed, embedded, imprinted, etched, grown, deposited orotherwise formed) in the volume of or on a surface of a substrate 10.The optical identification element 8 described herein is the same asthat described in Copending patent application Ser. No. 10/661,234,filed Sep. 12, 2003, which is incorporated herein by reference in itsentirety. The grating 12 may have a periodic or aperiodic variation inthe effective refractive index and/or effective optical absorption of atleast a portion of the substrate 10. It is important to note that thegrating shown and described herein is provided by way of example. Thescope of the invention is not intended to be limited to the type or kindof grating 12 in the substrate, the type or kind of variations formingthe same, or the manner or technique for disposing the grating 12 intothe substrate 10. Moreover, the scope of the invention is intended toinclude gratings and techniques for disposing the same both now known inthe art, as well as those developed in the future.

As shown, the substrate 10 has an inner region 20 where the grating 12is located. The inner region 20 may be photosensitive to allow thewriting or impressing of the grating 12. The substrate 10 has an outerregion 18, which does not have the grating 12 therein.

The grating 12 is a combination of one or more individual spatialperiodic sinusoidal variations (or components) in the refractive indexthat are collocated at substantially the same location on the substrate10 along the length of the grating region 20, each having a spatialperiod (or pitch) Λ. The resultant combination of these individualpitches is the grating 12, comprising spatial periods (Λ1-Λn) eachrepresenting a bit in the code. Thus, the grating 12 represents a uniqueoptically readable code, made up of bits, where a bit corresponds to aunique pitch Λ within the grating 12. Accordingly, for a digital binary(0-1) code, the code is determined by which spatial periods (Λ1-Λn)exist (or do not exist) in a given composite grating 12. The code orbits may also be determined by additional parameters (or additionaldegrees of multiplexing), and other numerical bases for the code may beused, as discussed herein and/or in the aforementioned patentapplication. However, it is important to note that the scope of theinvention is not intended to be limited to the type or kind of coderepresented by the grating 12, or the manner or technique for reading orinterpreting the same. Moreover, the scope of the invention is intendedto include the grating represent codes, and/or or the manner ortechnique for reading or interpreting the same, both now known in theart, as well as those developed in the future.

The grating 12 may also be referred to herein as a composite orcollocated grating. Also, the grating 12 may be referred to as a“hologram”, as the grating 12 transforms, translates, or filters aninput optical signal to a predetermined desired optical output patternor signal.

The substrate 10 has an outer diameter D1 and comprises silica glass(SiO₂) having the appropriate chemical composition to allow the grating12 to be disposed therein or thereon. By way of example, the substrate10 may be made of any glass, e.g., silica, phosphate glass, borosilicateglass, or other glasses, or made of glass and plastic, or solelyplastic; however, other materials for the optical substrate 10 may beused if desired, including materials now known or later developed in thefuture. For high temperature or harsh chemical applications, the opticalsubstrate 10 made of a glass material is desirable. If a flexiblesubstrate is needed, plastic, rubber or polymer-based substrate may beused. In effect, the optical substrate 10 may be any material capable ofhaving the grating 12 disposed in the grating region 20 and that allowslight to pass through it to allow the code to be optically impartedtherein and read within the spirit of the invention described herein.

The optical substrate 10 with the grating 12 has a length L and an outerdiameter D1, and the inner region 20 diameter D. The length L can rangefrom very small “microbeads” (or microelements, micro-particles, orencoded particles), about 1-1,000 microns or smaller, to larger“macrobeads” or “macroelements” for larger applications (about 1.0-1,000mm or greater). In addition, the outer dimension D1 can range from small(less than 1,000 microns) to large (1.0-1,000 mm and greater). Otherdimensions and lengths for the substrate 10 and the grating 12 may beused within the spirit of the invention described herein.

The grating 12 may have a length Lg of about the length L of thesubstrate 10. Alternatively, the length Lg of the grating 12 may beshorter than the total length L of the substrate 10. The scope of theinvention is not intended to be limited to any particular length Lg ofthe grating, or the length Lg in relation to the length L of thesubstrate 10. The outer region 18 is made of pure silica (SiO₂) and hasa refractive index n2 of about 1.458 (at a wavelength of about 1553 nm),and the inner grating region 20 of the substrate 10 has dopants, such asgermanium and/or boron, to provide a refractive index n1 of about 1.453,which is less than that of outer region 18 by about 0.005. Other indicesof refraction n1, n2 for the grating region 20 and the outer region 18,respectively, may be used, if desired, provided the grating 12 can beimpressed in the desired grating region 20. For example, the gratingregion 20 may have an index of refraction that is larger than that ofthe outer region 18 or grating region 20 may have the same index ofrefraction as the outer region 18 if desired. In other words, the scopeof the invention is not intended to be limited to any particularrefractive index of the inner or outer region, or the relationship ofthe refractive indices in relation to one another, or the materials ordopants used to provide the same in these regions, within the spirit ofthe invention.

FIG. 2 shows, by way of example, a technique for reading the code in theoptical identification element 8. As shown, an incident light 24 of awavelength λ, e.g., 532 nm from a known frequency doubled Nd:YAG laseror 632 nm from a known Helium-Neon laser, is incident on the grating 12in the substrate 10. Any other input wavelength λ can be used if desiredprovided the wavelength λ is within the optical transmission range ofthe substrate (discussed more herein and/or in the aforementioned patentapplication(s)). A portion of the input light 24 passes straight throughthe grating 12, as indicated by the arrow 25. The remainder of the inputlight 24 is reflected by the grating 12, as indicated by the arrow 27and provided to a detector 29. The output light 27 may be a plurality ofbeams, each having the same wavelength λ as the input wavelength λ andeach having a different output angle indicative of the pitches (Λ1-Λn)existing in the grating 12. Alternatively, the input light 24 may be aplurality of wavelengths and the output light 27 may have a plurality ofwavelengths indicative of the pitches (Λ1-Λn) existing in the grating12. Alternatively, the output light 27 may be a combination ofwavelengths and output angles. The above techniques are discussed inmore detail herein and/or in the aforementioned patent application. Itis important to note that the scope of the invention is not intended tobe limited to any particular input wavelength used, or the number ofwavelengths used, or the number of beams used, or the angle of the beamsused, in the technique for reading the code in the opticalidentification element 8 within the spirit of the invention.

The detector 29 has the necessary optics, electronics, software and/orfirmware to perform the functions described herein. In particular, thedetector reads the optical signal 27 diffracted or reflected from thegrating 12 and determines the code based on the pitches present or theoptical pattern, as discussed more herein or in the aforementionedpatent application. An output signal indicative of the code is providedon a line 31. Optical detectors like 29 are known in the art, and thescope of the invention is not intended to be limited to any particulartype or kind thereof.

The Grating Writing Process

The diffraction grating(s) 12 may be written or shot, for example, inthe manner shown and described in detail in the technique shown anddescribed in the aforementioned patent application Ser. No. 10/661,234filed Sep. 12, 2003, which is incorporated herein by reference in itsentirety. The grating 12 may be impressed in an optical fiber orsubstrate by any technique for writing, impressed, embedded, imprinted,or otherwise forming a diffraction grating in the volume of or on asurface of a substrate now known or later developed in the future.Examples of some known techniques are disclosed in U.S. Pat. Nos.4,725,110 and 4,807,950, entitled “Method for Impressing Gratings WithinFiber Optics”, issued to Glenn et al; and U.S. Pat. No. 5,388,173,entitled “Method and Apparatus for Forming Aperiodic Gratings in OpticalFibers”, issued to Glenn, respectively; and U.S. Pat. No. 5,367,588,entitled “Method of Fabricating Bragg Gratings Using a Silica GlassPhase Grating Mask and Mask Used by Same”, issued to Hill; and U.S. Pat.No. 3,916,182, entitled “Periodic Dielectric Waveguide Filter”, issuedto Dabby et al; and U.S. Pat. No. 3,891,302, entitled “Method ofFiltering Modes in Optical Waveguides”, also issued to Dabby et al.,which are all hereby incorporated herein by reference to the extentnecessary to understand the present invention.

Alternatively, instead of the grating 12 being impressed within thefiber material, the grating 12 may be partially or totally created byetching or otherwise altering the outer surface geometry of thesubstrate to create a corrugated or varying surface geometry of thesubstrate, such as is disclosed in U.S. Pat. No. 3,891,302, entitled“Method of Filtering Modes in Optical Waveguides”, issued to Dabby etal., which is also hereby incorporated herein by reference to the extentnecessary to understand the present invention, provided the resultantoptical refractive profile for the desired code is created.

Further, alternatively, the grating 12 may be made by depositingdielectric layers onto the substrate, similar to the way a known thinfilm filter is created, so as to create the desired resultant opticalrefractive profile for the desired code.

FIG. 3

In one experiment, an optical identification element was exposed to 7collocated gratings and interrogated from the side in the mannerdescribed in U.S. patent application Ser. No. 10/661,234 filed Sep. 12,2003 incorporated herein by reference. Resulting diffracted beams 58were imaged and read using a CCD camera like device 60 in FIG. 3 and theimages were captured and processed using a frame grabber card in apersonal computer (PC) or other suitable processing device, not shown.The Bragg envelope for the two optical identification elements were alsomeasured by capturing the images of the diffracted beams for a range ofrotation angles. It was found that under normal exposure conditions, theexcess Boron in the core provided enhanced photosensitivity over thestandard “photosensitive” telecom fiber. FIG. 3 shows the laser 52providing an input light beam 54 on two elements 56 a, 56 b, and anoutput beam 58 being read by the CCD camera 60.

FIG. 4

FIG. 4( a) shows a schematic of the fiber geometry of an optical fiberor substrate 100 having a core 102 with a grating 103 and also having acladding 104. As shown, the core 102 has a length L of about 10 μm andthe grating 103 has a pitch of about 0.5 μm. In response to an opticalsignal having a wavelength λ=632 nanometers (nm) received at an angleΘ_(i), the grating 103 provides a reflected optical fiber at an angleΘ_(o) with respect to the normal consisting of a plurality of uniquelydistinguishable signals covering an angle range of Θ^(R). The index ofrefraction of the cladding and core respectively are 1.458 and 1.455(i.e. difference of 0.003). The reader is also referred to the graph inFIG. 5.

SCOPE OF THE INVENTION

Although the invention has been described and illustrated with respectto exemplary embodiments thereof, the foregoing and various otheradditions and omissions may be made therein and thereto withoutdeparting from the spirit and scope of the present invention.

1. A non-waveguide optical identification element comprising anon-waveguide optical substrate that includes an inner region located ata geometric center of the optical substrate, the inner region beingsurrounded by an outer region, the inner region having an index ofrefraction that prevents the optical substrate from forming an opticalwaveguide, the optical substrate having an identification code impartedtherein, wherein the inner region is a photosensitive optical region. 2.The non-waveguide optical identification element according to claim 1,wherein the identification code is written in the optical substrate as aBragg grating.
 3. The non-waveguide optical identification elementaccording to claim 1, wherein the identification code is written in theinner region.
 4. The non-waveguide optical identification elementaccording to claim 1,wherein the identification code is written in theouter region.
 5. The non-waveguide optical identification elementaccording to claim 1, wherein the inner region has an index ofrefraction less than or equal to the outer region.
 6. The non-waveguideoptical identification element according to claim 1, wherein the outerregion is a non-photosensitive optical region.
 7. The non-waveguideoptical identification element according to claim 1, wherein the innerand outer regions have indices of refraction that differ from oneanother in a manner that prevents the optical substrate from forming anoptical waveguide.
 8. The non-waveguide optical identification elementaccording to claim 1, wherein the index of refraction of the outerregion is uniform throughout the outer region.
 9. The non-waveguideoptical identification element according to claim 1, wherein the outerregion has a common index of refraction as measured radially outwardfrom the geometric center of the optical substrate.
 10. Thenon-waveguide optical identification element according to claim 1,wherein the outer region includes a coded portion containing theidentification code and wherein the index of refraction is uniformthroughout the outer region outside of the coded portion.
 11. Thenon-waveguide optical identification element according to claim 1,wherein the index of refraction of the inner region along the interfaceis less than the index of refraction of the outer region along theinterface to prevent the optical substrate from forming an opticalwaveguide.
 12. The non-waveguide optical identification elementaccording to claim 1, wherein the inner region constitutes a solidsubstrate.
 13. The non-waveguide optical identification elementaccording to claim 1, wherein at least one of the inner and outerregions includes the identification code imparted therein.
 14. Anon-waveguide optical identification element comprising an inner regionbeing surrounded by an outer region, the inner region being located at ageometric center of the element and having an index of refraction thatis less than or equal to an index of refraction of the outer region, theelement having a Bragg grating inscribed therein, wherein the innerregion is a photosensitive optical region.
 15. The non-waveguide opticalidentification element according to claim 14, wherein the outer regionis a non-photosensitive optical region.
 16. The non-waveguide opticalidentification element according to claim 14, wherein the photosensitiveoptical region is doped with Boron.
 17. The non-waveguide opticalidentification element according to claim 14, wherein the photosensitiveoptical region is doped with excess amounts of Boron when compared to anamount of doping used for a standard telecom optical fiber.
 18. Thenon-waveguide optical identification element according to claim 14,wherein the index of refraction of the outer region is uniformthroughout the outer region.
 19. The non-waveguide opticalidentification element according to claim 14, wherein the outer regionhas a common index of refraction as measured radially outward from thegeometric center of the optical substrate.
 20. The non-waveguide opticalidentification element according to claim 14, wherein the outer regionincludes a grating portion containing the Bragg grating and wherein theindex of refraction is uniform throughout the outer region outside ofthe Bragg grating.
 21. The non-waveguide optical identification elementaccording to claim 14, wherein the index of refraction of the innerregion along the interface is less than the index of refraction of theouter region along the interface to prevent the optical substrate fromforming an optical waveguide.
 22. The non-waveguide opticalidentification element according to claim 14, wherein the inner regionconstitutes a solid substrate.
 23. The non-wave guide opticalidentification element according to claim 14, wherein at least one ofthe inner and outer regions includes the Bragg grating inscribedtherein.
 24. A microbead comprising a non-waveguide optical elementhaving a photosensitive core surrounded by a non-photosensitivecladding, the photosensitive core being located at a geometric center ofthe optical element and having an index of refraction that is less thanor equal to an index of refraction of the non-photosensitive cladding soas not to form an optical waveguide, and the photosensitive core alsohaving a Bragg grating inscribed therein.
 25. A microbead according toclaim 24, wherein the photosensitive core is doped with Boron.
 26. Amicrobead according to claim 24, wherein the photosensitive core isdoped with excess amounts of Boron when compared to a standard telecomoptical fiber.